The background description provided herein is for the purpose of generally presenting the context of the disclosure. All description and statements in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In automotive industry, the areas of major technology development nowadays include vehicle safety, energy saving and environmental friendliness, as well as intelligent electronics. Vehicle brake system is an inseparable part of vehicle safety, and has received high degree of attention. In the recent years, in addition to wide application of antilock brake system (ABS), stability enhancement system and brake assistance system (BA) in many lines of vehicle production, the adaptive cruise control (ACC) and active collision avoidance systems have also been applied to varieties of vehicle platforms, demanding an ever enhanced requirement of brake systems.
With technology advancement in electronic controls reaching an unprecedented level, by-wire control technology also enjoys the fruit of its leading-edge development. In the area of brake control system, the electro-hydraulic brake system (EHB), the electro-mechanical brake system (EMB) and integrated brake system (IBS) have been developed and implemented in production vehicles with various forms of configuration. Due to elimination of mechanical linkages between components of a traditional brake system, the by-wire brake control system has advantages of more flexible control, simpler configuration, shorter response time, better braking performance, easier maintenance, and so forth, thus becomes a better candidate for implementing the active cruise control (ACC), active collision avoidance and regenerative braking control systems.
In pressure-increase phase of an electro-hydraulic brake system (EHB), the switching valve connected to piston cylinder is first closed, followed by opening of the wheel cylinder inlet valves. Brake fluid flows into the wheel cylinder via the inlet valves from a pressure chamber of the piston cylinder through hydraulic circuit. In pressure-reduction phase, inlet valves are closed, and outlet valves are open. Brake fluid flows from wheel cylinder back to the reservoir. In pressure-retention phase, both inlet valves and outlet valves are closed. While there is fault detected in hydraulic circuit, the switching valve is maintained at an open state so as to facilitate brake fluid to flow from piston cylinder to wheel cylinder via the switching valve and inlet valve. In EHB system, the energy for brake actuation is provided by the pressure storage chamber, and it has advantage of fast response. However, the system requires a more sophisticated hydraulic circuit and more number of electro-magnetic valves.
In an electro-mechanical brake system (EMB), vehicle braking is realized via brake caliper clamping on brake discs, which is caused by a motion of controlled motor rotation, which is transferred to the clamping action, based on a brake pedal signal. Such system has advantages of fast response, easier control implementation and feasibility for by-wire implementation. However, it is more difficult to implement back-up functionality under a system failure condition.